1. Field of the Invention
The present invention relates to a fuel cell system which can recover pressure energy from an exhaust gas by expanding the exhaust gas in a regenerator after oxygen has been consumed in a fuel cell and use the recovered energy to assist in driving a compressor.
2. Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 7-14599 discloses a fuel cell system. FIG. 5 in the attached drawings shows such a prior art, wherein air sucked through an air feeding conduit 60 is supplied to a fuel cell 63 after being pressurized to a certain pressure by a compressor 62 driven by an electric motor 61. Oxygen is consumed from the supplied air in the fuel cell and an exhaust gas is discharged from the system to the atmosphere after being expanded in an expander 65 coupled to the compressor 62 and the motor 61 with a common shaft 64.
The produced water contained in the exhaust gas is separated by liquid separators 67 and 68 provided in an air discharging conduit 66, and collected into an open type reservoir 69, from which the stored water is fed to a jet nozzle 71 by a pump 70 and injected into the air feeding conduct 60 for the purpose of humidifying the process air.
That is, as stated above, it is very efficient for the produced water contained in the exhaust gas from the fuel cell 63 to be separated and collected for the purpose of humidifying the process air. Such water is usable not only for maintaining the proton conductivity of a cation exchange membrane in the fuel cell 63 but also for cooling and lubricating the compressor 62. In this respect, a scroll type compressor particularly could benefit from the use of such water, and there have been many proposals for improving the scroll type compressors or expanders.
However, when the residual (pressure) energy remaining in the exhaust gas from the fuel cell is converted to a mechanical energy by the regenerator (expander) and fed to the compressor via the common shaft, a difference is generated between the pressure of the discharge air from the compressor and the pressure of the exhaust gas introduced into the regenerator due to a pressure loss in the fuel cell, whereby the exhaust gas is sometimes made to expand in the regenerator to have a subatmospheric pressure, resulting in an undesirable energy consumption.
An object of the present invention is to solve the above-mentioned problem in the prior art while maintaining the merits of a scroll type compressor and a scroll type regenerator, by recovering the residual energy from the exhaust gas of a fuel cell to assist the compressor without useless power consumption in the regenerator as well as to further improve in the mechanical efficiency by simplifying the structure of the compressor and the regenerator of a scroll type.
A fuel cell system, according to the present invention, to solve the above problems, comprises: a fuel cell having an air feeding passage and a gas exhaust passage; a scroll type compressor arranged in the air feeding passage, said compressor including a stationary scroll and a movable scroll; a scroll type regenerator arranged in the gas exhaust passage, said regenerator including a stationary scroll and a movable scroll; a motor having an output shaft; the movable scroll of the compressor being integrally formed with the movable scroll of the regenerator such that the movable scroll of the compressor and the movable scroll of the regenerator have a common base plate, a first scrolling wall extending on one side of the common base plate and a second scrolling wall extending on the opposite side of the common base plate; the first scrolling wall being engaged with the stationary scroll of the compressor, the second scrolling wall being engaged with the stationary scroll of the regenerator; and the common base plate being operatively coupled to the output shaft of the motor.
Since the compressor and the regenerator, both of which are of a scroll type, are skillfully combined with each other via the common movable scroll coupled to the motor output shaft, an air feeding mechanism having a strict simplicity and an excellent mechanical efficiency as required particularly for a vehicle fuel cell system, can be obtained. If the pressure ratio of the regenerator is set to a value capable of sufficiently compensating for a pressure loss of the supplied air generated in the fuel cell, it is possible to prevent the exhaust gas introduced into the regenerator excessively expanding to a subatmospheric pressure; in other words, the transmission of negative torque due to the rotation of the regenerator to the motor output shaft is completely avoidable to facilitate the effective assistance to the compressor.
If the system is adapted so that the water separated from the exhaust gas is pumped to the injector of the scroll type compressor, it is possible not only to humidify the supplied air but also to suitably cool and lubricate the compressor itself. Also, if both the compressor and the regenerator are arranged in phase so that peaks of torque variation thereof generally coincide with each other, the power transmission between the compressor and the regenerator is further enhanced. Moreover, if the number of turns of the scrolling walls formed in the scroll of the compressor and the regenerator is adjustable, it is possible to easily select a suitable relative pressure ratio between the both in correspondence to the pressure loss within the fuel cell.